MdeModulePkg/UsbKb: Don't access key codes when length is wrong

Per USB HID spec, the buffer holding key codes should be 8-byte
long.
Today's code assumes that the key codes buffer length is 8-byte
long and unconditionally accesses the key codes buffer.
It's incorrect.
The patch fixes the issue by returning Device Error when the
length is less than 8-byte.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ruiyu Ni <ruiyu.ni@intel.com>
Cc: Star Zeng <star.zeng@intel.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Steven Shi <steven.shi@intel.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>

MdeModulePkg/Bus/Usb/UsbKbDxe/KeyBoard.c

@@ -1059,6 +1059,10 @@ KeyboardHandler (
   // Byte 1 is reserved.
   // Bytes 2 to 7 are keycodes.
   //
+  if (DataLength < 8) {
+    return EFI_DEVICE_ERROR;
+  }
+
   CurKeyCodeBuffer  = (UINT8 *) Data;
   OldKeyCodeBuffer  = UsbKeyboardDevice->LastKeyCodeArray;